The present invention relates to a system for deploying moveable wing surfaces, for example aircraft slats and flaps.
Various mechanisms have been proposed for deploying slats and flaps, including paired track systems, Kruger flap systems and swing arm systems. The present invention is applicable to a swing arm system, for example of the general type described in International patent application No: PCT/NZ95/00096, the content of which is incorporated by reference herein. The invention is also applicable to other deployment systems including, for example, the system described in U.S. Pat. No. 5,651,513 (Arena), the content of which is also incorporated herein by reference, which employs a torsion bar and sway bar mechanism. The deployment system may be used for deploying slats or flaps and in the following description references to slat deployment systems are intended to include flap deployment systems, and vice versa.
During takeoff, the best condition for the wing is to have high camber, but low drag.
During landing, drag is not such a concern, but high lift and low speed are priorities. During cruise, minimising drag is the highest priority. Lift coefficients are much lower, as speed is much greater; therefore camber is very low.
During a long flight the weight of an aircraft will change significantly causing the need for the wings to vary their lift, given the same speed and altitude. The normal method to do this is to change the angle of attack: the angle of the wing plane to the horizon. However, this necessarily causes the profile of the aircraft to increase, with detrimental affects to the drag and fuel burn.
One way to minimise drag whilst changing the lift coefficient of the wings is to employ variable camber to the wing. The variation of camber can best be achieved when both surfaces are contiguous, giving minimum drag. Variable camber can be achieved at either the leading or trailing edge, or both.
For landing, providing a slot in the wing surface ensures airflow attachment to the top surface with high angles of attack. This provides high lift but at the cost of high drag. This can be beneficial during landing, to ensure low speed and controlled descent.
For take-off it is most important to gain speed and the additional drag of a slot is not beneficial. In fact it is normal to deploy less camber due to the penalties of lift induced drag.
It is an object of the present invention to mitigate at least some of the above problems, or at least provide an alternative to the current systems.
According to a first aspect of the present invention there is provided a wing including a main wing section and a moveable wing surface that is adjustable relative to an adjacent edge of the main wing section to alter the camber of the wing, wherein the adjacent edge of the main wing section is shaped such that the moveable wing surface remains substantially in contact with the main wing section when the moveable wing surface is positioned between a fully retracted condition and a partially deployed condition, and a slot is provided between the moveable wing surface and the main wing section when the moveable wing surface is positioned between the partially deployed condition and a fully deployed condition.
By analysis it is possible to plot the trailing edge of the slat during its motion forward. If this loci of points is used as a template to design the leading edge surface of the main wing, it is possible to ensure a contiguous contact with the trailing edge of the slat for a large proportion of the deployment. If this system of design is used until takeoff position, this ensures low drag throughout this envelope. Further, at maximum deployment of the slat, during landing, the slat loses contact with the leading edge of the main wing, to develop a slot, which permits higher levels of camber, and more lift for a given speed.
This also means that the surface between the slat and main wing only comes into play during landing, when drag losses are less important. Thus, there is less requirement for a smooth, aerodynamic profile between the slat and main wing. Therefore complex shutter mechanisms do not need to be employed to improve the aerodynamics of the flow through the slot.
Advantageously, the moveable wing surface is positioned between a fully retracted condition and the partially deployed condition when the wing is set in a condition suitable for take off or cruising flight, and the moveable wing surface is positioned between the partially deployed condition and a fully deployed condition when the wing is set in a condition suitable for landing.
According to one embodiment of the invention, the moveable wing surface is a slat and the adjacent edge is the leading edge of the main wing section. Advantageously, the upper surface of the main wing section leading edge is shaped to remain substantially in contact with the upper trailing edge of the slat, when the slat is positioned between a fully retracted condition and the partially deployed condition.
The main wing section may include a closure mechanism for closing a gap in the underside of the wing between the main wing section and the moveable wing surface, during at least part of the movement of the moveable wing surface from the fully retracted condition to the partially deployed condition.
According to a second aspect of the present invention there is provided a wing including a main wing section and a moveable wing surface that is adjustable relative to an adjacent edge of the main wing section to alter the camber of the wing, in which the main wing section includes a closure mechanism for closing a gap in the underside of the wing between the main wing section and the moveable wing surface, during at least part of the movement of the moveable wing surface.
The closure mechanism may include a panel hinged to the lower surface of the main wing section. The panel may be resiliently biassed.
The moveable wing surface may include connection means for engaging the closure mechanism during at least part of the movement of the moveable wing surface from the fully retracted condition to the partially deployed condition, to control movement of the panel. The connection means may include a releasable tongue and grove joint.
Alternatively, the wing may include drive means for controlling operation of the closure mechanism.
The moveable wing surface may be connected to the main wing section by a swing arm mechanism or by a sway bar and torsion bar mechanism. Operation of the closure mechanism may then be controlled by one or more links from components of the swing arm mechanism or the sway bar and torsion bar mechanism.
By hinging the lower surface of the main wing near to the front spar and attaching the forward end of that surface to the trailing edge of the slat, it is possible to gain a contiguous lower surface, over a small range of slat movement. This small range is consistent with the needs of variable camber during cruise conditions.
One way of attaching the lower surface of the main wing to the slat trailing edge is by spring force, such that the lower surface of the main wing, the hinged panel, is pushed until it meets the lip of the trailing edge of the slat.
Another method of attaching the lower surface to the slat is to have grove in the slat trailing edge which intersects with a tongue on the lower surface of the hinged panel(s).
The movement of the hinged panel(s) is limited by an end stop, such that when the slat deploys further, for takeoff or landing, a gap appears in the lower surface between the slat and the main wing. On retraction of the slat the trailing edge of the slat re-engages the tongue in the lower surface of the main wing.
Another embodiment would be a fully mechanical deployment system for the hinged panels. If the main slat system were a swing arm type, it would be possible to deploy the hinged panel(s) by a link from the swing arm to the hinged panel.